1. Field of the Invention
The invention relates to a process for preparing a concentrate of human plasma Factor XI having very high specific activity and intended for therapeutic use.
2. Description of Related Art
Factor XI or the precursor of plasma thromboplastin, is a glycoprotein that forms part of the contact phase, in the hemostasis mechanism, through its Factor IX activating effect and, on the other hand, of the fibrinolytic system through its plasminogen activating effect.
Factor XI deficiency is hereditary and is transmitted as a recessive autosomal character. This is a rare deficiency but one that is widespread in certain populations of the Middle East.
As with other factors in which a deficiency is rare (Factors V, XIII, X), therapeutic products purified from human plasma are nonexistent or rare, and the only replacement treatment is carried out using total plasma or the supernatant fraction of the cryoprecipitated plasma, but this entails the simultaneous injection of useless quantities of other plasma proteins, hence a risk of various major secondary reactions after multiple injections.
The purification of Factor XI, on an experimental scale, was difficult to achieve, and then, only with the use of powerful inhibitors, which suggests that this molecule is highly labile. Purification was carried out in a series of 4 or 5 steps of ion exchange chromatography and affinity chromatography, either starting from plasma (Bouma and Griffin, 1977, J. Biol. Chem. 252, 6432-6437) or from platelets (Schiffman and Yeh, 1990, Thromb. Res. 60, 87-97). A highly purified bovine Factor XI was also purified from 20 liters of plasma by precipitation and chromatographic steps in about 9 days (Koide et al., 1975, in: Methods in Enzymology--Blood Clotting Enzymes, pp. 65-73). Only one preparation having a quality compatible with therapeutic use has been described (Winkelman et al., 1988, Internat. Congress ISBT-BBTS London), and was obtained by adsorption on heparin-sepharose after recovery of Factors VIII and IX, but its specific activity does not exceed 5 U/mg of protein, and contains high doses of residual AT III. Applicants are aware of no other process of preparing Factor XI which allows for production on an industrial level, and which provides larger quantities of Factor XI of suitable quality for therapeutic use on a large scale.